Bimetallic strip thermostat

ABSTRACT

A BIMETALLIC STRIP THERMOSTAT HAVING A MOUNTING OF TWO ABUTMENTS ON OPPOSITE MAJOR FACES OF THE STRIP AND SPACED LONGITUDINALLY OF EACH OTHER. A RESILIENT HOLD-DOWN ELEMENT ENGAGES THE STRIP IN REGISTRY WITH ONE OF THE ABUTMENTS AND ON THE OPPOSITE FACE THEREOF FROM THAT ENGAGED   BY THE ABUTMENT TO SUSTAIN THE STRIP WITH A FREE END REMOTE FROM THE ABUTMENT ADAPTED TO BE DISPLACED THERMALLY.

Jan. 12, 1971 D. H. CALLIHAN BIMETALLIC STRIP THERMOSI'AI Filed April14, 1969 r 36 27 38 4 25 1s 6 I a;

INVENTOR.

DALE H. CALLIHAN ATTORNEYS United States Patent 3,555,482 BIMETALLICSTRIP THERMOSTAT Dale H. Callihan, Huron, Ohio, assignor to NorwalkThermostat "Company, Norwalk, Ohio, a corporation of Ohio Filed Apr. 14,1969, Ser. No. 815,863 Int. Cl. H01h 37/20, 37/52 U.S. Cl. 337-360 7Claims ABSTRACT OF THE DISCLOSURE SUMMARY OF THE INVENTION Thisinvention relates to bimetallic strip thermostats and more particularlyto the mounting for such thermostats.

Heretofore it has been known to mount bimetallic strip thermostats atthree locations along their length by locating a portion of a firstmajor face of the strip at its actuating end on a member to be actuated,engaging an intermediate portion of the strip on a second major facewith an abutment, and engaging a third portion of the strip spaced fromthe actuating portion of the first major face with an abutment. In sucharrangements, some mechanical stress is imposed on the actuating end ofthe strip tending to deflect the strip from its unstressed condition inorder to maintain it in a mechanically stable relationship in itsmounting. Prebias by mechanical stressing is frequently undesirable aswhere the actuated member responds to light pressures and where thethermomechanical characteristics of the strip are distorted bystressing.

According to the present invention, bimetallic strip thermostat elementsare mounted on a pair of abutments with a resilient hold-down element tomaintain the strip against one of the abutments. In a preferredembodiment, the strip is formed with a convex face engaging an abutmentbetween its region providing the thermostatic action and the secondabutment. The second abutment engages an opposite face of the strip witha convex region. Adjustment of the strip around the intermediateabutment is afforded by adjusting the position of the second abutment ina direction normal to the face of the strip. The strip is supported as acantilever from the two abutments by providing a spring finger extendingas a cantilever from the intermediate abutment to the second abutmentand terminating in a bifurcated end. Each hold-down end terminates in afoot of arcuate form having a radius of curvature greater than that ofthe strip region registering along the length of the strip with theabutment whereby the foot engages the face of the strip opposite and inthe region of registry with the second abutment at two positions alongits length. Movement of the second abutment thus is followed by thebimetallic strip to produce an opposite motion of the actuating regionof the strip.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of one form ofbimetallic strip and its mounting as employed in an electrical snapaction switch assembly;

FIG. 2 is a plan of the switch assembly of FIG. 1;

FIG. 3 is an end view of the switch assembly of FIG. 1 taken from theright as viewed in FIG. 1;

FIGS. 4 and 7 are fragmentary side elevations of modified bimetallicassemblies showing the hold-down;

ICC

FIGS. 5 and 8 are plans of FIGS. 4 and 7 respectively: and

FIGS. 6 and 9 are end views of FIGS. 4 and 7 respectively taken from theright.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT The thermostat shown inFIG. 1 is the actuating means for an electrical switch 11 as disclosedin W. T. Watson Pat. 3,366,756 which issued Jan. 30, 1968, for SnapAction Assembly. It comprises an insulating housing 12 having electricalterminals 13 and 14 and an actuating plunger 15 responsive to very lightpressures normal to the upper face of housing 12 to transfer circuitconditions of the switch elements (not shown) within the housing. Switch11 is mounted on a base 16 of channel form by means of rivets or othersuitable post-like fasteners 17 and 18 and is electrically spacedtherefrom, particularly at its terminals by the fiberboard sheet 19.Base 16 is secured to a two-legged bracket 21 having spaced feet withthreaded bosses 22 for screw mounting the assembly.

Switch plunger 15 is moved toward and away from housing 12 by theactuating region 23 of a bimetallic strip 24 mounted on post 25extending through a suitable aperture (not shown) in the strip. A head26 on post 25 having a flat underface forms an abutment upon which theconvex region 27 of the upper face of strip 24 rocks as a fulcrum forthe strip. A region 28 of strip 24 spaced from actuating region 23 byfulcrum 27 engages an abutment 29 which can be a washer mounted on thereduced end of post 32 in abutting engagement with shoulder 33. Theregion 28 of engagement of strip 24 with abutment 29 is on the oppositemajor face of the strip from that which engages abutment 26 and isconvex in form to provide a rolling contact.

Stability of the mounting of strip 24 is afforded by a hold-down 34having a bifurcated end with each foot engaging the strip generally inlongitudinally aligned registry along the strip with abutment 29 on theface opposite its contact with strip 24 and resiliently biased towardstrip 24.

The hold-down 34 is bifurcated, as best seen in FIG. 2, to straddle andclear the protuberance projecting through strip 24 from abutment 29. Itis cylindrical and has an arcuate form with an outer radius of curvaturegreater than the inner radius of curvature of the strip region 28. This,by virtue of the upstanding tail portion 35 of strip 24, provides twobearing points longitudinally spaced along strip 24 for hold-down 34 oneach side of the strip as at 36 and 37 in FIG. 1. Hold-down 34 includesa cantilever spring 38 secured between the underside of the rivet 18 andthe head 26 of post 25 to resiliently bias the foot toward abutment 29.

Strip 24 is arranged to engage the first abutment 26, that intermediatethe actuating end and the second abutment 29, and the second abutment 29with a rocking or rolling contact to enable smooth motion of theactuating end. Further, the strip is apertured to accommodate posts 25and 31 extending from abutments 28 and 29 respectively. These aperturesare of an extent to provide freedom around the posts and are of lessextent than the abutments so that adequate bearing surfaces are providedfor strip support.

Abutment 29 is adjustable by virtue of the threads (not shown) on post32 within internally threaded collar or nut 39. Collar 39 is maintainedagainst the upper face of base 16 by swedging a reduced section whichpasses through accommodating, registering apertures (not shown) in thebase 16 and bracket 21 against the walls of those apertures. Backlashand any tendency to slip out of adjustment by rotation of post 32 incollar 39 is avoided by a helical spring 41 abutting the lower face ofthe base and concentrically mounted on post 32 to provide a brakingaction by imposing tension on stem 32 and loading the threadedconnection to collar 39. A washer 42 abuts the opposite end of spring 41and is held on post 32 by a snap washer 43. Tubular stem 44 secured topost 32 protrudes beyond the feet of mounting bracket 21 and is cut awayon one side at 45 to facilitate mounting a control knob or the like (notshown). Upon completion of the assembly of the switch, bimetal strip,hold-down, and adjustable abutment, the operating points for the switchare established. Collar 39 is provided with a permanent stop 40, anupstanding stub on its upper surface as viewed in FIGS. 1 and 3. Acooperating stop 46 is secured on post 32 to limit its range of rotationby engagement with stub 40. The position of stop 46 is established bysubjecting the assembly to the temperature desired for an operatingpoint at a limit, rotating the post 32 until bimetal strip 24 is shiftedto a position to move plunger to cause the desired operation of switch11 and then spot welding stop 46 to the adjusted shaft 32 while indexedagainst stub 40. With proper design of the bimetal and matching to theswitch 11 and range of adjustment of post 32, the thermostatic switchwill otfer a range of operating points dependent upon the degree ofrotation of post 32.

In operation, the strip 24 flexes while offering some rolling contactwith abutments 26 and 29 to move actuating region 23 upward or downwardwith changes in temperature. The critical position at which switch 11 isoperated by such movement is reached at varying temperatures dependingupon the positioning of abutment 29, as is readily understood by thoseskilled in the thermostat art.

Other forms of hold-downs for an assembly as shown in FIGS. 1 to 3 areshown in FIGS. 4 through 9. The two lines of tangency of the cylindricalfoot 34 with the concave region 28 of strip 24 in the vicinity ofabutment 29 provides stability to the strip by maintaining it inengagement with abutment 26 at region 27 and abutment 29 at region 28.Similar relationships are maintained in FIGS. 3 through 6 by engagementof the ends 51 of a spring 38 centered over the line of tangency ofregion 28 with abutment 29. The pressure of the ends 51 upon the concavesurface registering longitudinally of the strip 24 insures that thestrip is maintained in place on movable abutment, both in the directionof motion of the abutment and laterally of the strip as permitted by theclearances in the apertures in the strip through which posts and 32extend.

A further interlocking of the hold-down with the bimetallic strip can beachieved by the embodiment of FIGS. 7 through 9 wherein like elementshave the reference characters of FIG. 1 double primed. In thisembodiment, the bifurcated ends 61 and 62 on cantilever spring 38"having protruding tongues 63 and 64 which fit into slots 65 and 66 instrip 24" which register longitudinally thereof with the region 28"engaging abutment 29. In this arrangement, the tongues 63 and 64 augmentthe mechanical connection offered by the down turned portion of ends 62and 63 which engage the concave surface registering longitudinally ofstrip 24" with the region engaging abutment 29. In each type ofhold-down balance around the second abutment transverse of the strip isassured since the transverse spacing of the areas of engagement of theends is equally spaced around the centerline of the assembly.

It is to be appreciated that the hold-down can be mounted other than onthe rivet supporting the intermediate abntrnent, that the intermediateabutment can be made adjustable and that reversals of functions can bemade wherein the abutment for the distal end of the bimetallic strip isfixed and the intermediate abutment adjustable. In the latterarrangement, the hold-down can impose force on the intermediateabutment. In view of the many variants and modifications in thestructure which are possible, it should be recognized that the abovedisclosure is illustrative of the invention and is not to be read in alimiting sense.

What is claimed is:

1. A bimetallic strip having a first and second major face; a firstconvex region transverse of the length of said strip and extending fromsaid second major face; a second convex region transverse of the lengthof said strip and extending from said first major face; a firstgenerally planar abutment engaging said first convex region; a secondgenerally planar abutment engaging said second convex region; said firstand second abutments cooperating with said respective engaging convexregions to provide a low friction floating support for said strip,whereby said convex regions have a rolling motion upon their respectiveabutments when said strip is moved relative to said abutments inresponse to said thermal changes imposed on said strip; a base carryingsaid first and second planar abutments; an element secured to said basefor actuation by said strip; an actuating portion on the first face ofsaid strip spaced from said first and second convex regions andpositioned to displace said element in response to thermal changesimposed on said strip; and a resilient hold-down supported in fixedrelationship to said base, a strip engaging portion of said hold-downlocated in registry with one of said convex regions and engaging saidstrip on the face opposite said abutment engaged by said one convexregion to bias said strip toward said abutment, and all portions of saidhold-down other than said strip engaging portion being spaced from saidstrip.

2. A combination according to claim 1 including means to adjust one ofsaid abutments in a direction normal to the major face of said stripengaged thereby.

3. A combination according to claim 2 wherein said adjusting means isfor said second abutment.

4. A combination according to claim 1 wherein said hold-down is acantilever spring.

5. A combination according to claim 1 wherein said hold-down is securedto one of said abutments and extends to the region in registry with theother of said abutments.

6. A combination according to claim 1 wherein each of said regions havea concave cylindrical surface on the major face of said strip oppositesaid convex cylindrical surface, said hold-down includes a convexcylindrical portion registering with one of said concave cylindricalregions and having a radius of curvature greater than said concaveregion whereby said hold-down engages said concave region along twospaced lines of contact transverse to the length of said strip.

7. A combination according to claim 1 wherein said strip has first andsecond apertures registering respectively with said first and secondabutments and of lesser extent than said abutments, a first protuberanceextending from said first abutment and having a cross-sectional arealess than said first aperture, and a second protuberance extending fromsaid second abutment and having a crosssectional area less than saidsecond aperture.

References Cited UNITED STATES PATENTS 8/1966 BletZ 337-347 5/1958 Weber337--372.(X)

U.S. Cl. X.R. 337372

